U of S | Mailing List Archive | alt-photo-process-l | Re: Unknown area in Gum printing?

Re: Unknown area in Gum printing?

Hmm... while this is good advice, to determine exposure time for each emulsion by use of a step wedge, and in fact is the first advice I gave Jacek in response to a private inquiry about gum printing a couple of months ago or so, I'm puzzled by the comment about "the correct DMax" being a function of the correct exposure. I would say that once he's settled on an exposure time for the emulsion by using a step wedge, then he's got one variable out of the way. But the DMax is the DMax, is determined by the pigment mix (beyond a certain minimal exposure, of course) and as is evident in the color apparent in the blocked "shadows" from 60% or so on in both 8 min and 12 min, is maxed out for this emulsion at a barely charcoal gray (hence my comment that the emulsion is underpigmented for lamp black).

Determining pigment concentration is the most difficult question facing beginners, in my experience, and each printer has to decide what method makes sense to him/her. I prefer to mix my stock mixes by eye to match a standard swatch, because that ensures maximum color saturation for each pigment, while mixing all pigments in the same proportions results in differences in how saturated each pigment is, so doesn't make sense to me. It's a matter of personal preference which one chooses, although a series of tests I did last fall and will upload to my website eventually, suggests that standardizing on color saturation makes calibration for digital negatives more consistent across pigments. But certainly I agree with Michael that a stock mix of some sort, at any rate, will make it easier to calibrate your process.

On Apr 26, 2007, at 2:02 PM, Michael Koch-Schulte wrote:


Where's the Stouffer stepwedge you shot with these test prints? You do own a Stouffer wedge r-i-i-i-ight? ^) Until you shoot that you have no idea if you're getting the correct dMax in the print. I routinely shoot my gums at 14 minutes for many, but not all colours. The time used is based on how they test with the wedge. Also, if you're calibrating your negatives using an imagesetter you might want to consider making a stock pigment/gum mix at this point and then adding equal amounts of potassium dichromate, gum and water to that.


Did that work?!
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----- Original Message -----
From: Jacek
To: alt-photo-process-l@usask.ca
Sent: Thursday, April 26, 2007 12:24 AM
Subject: Unknown area in Gum printing?

Hi all,

I tried my second attempt. Just a basic outline first on what I did.
Arches smooth 300gsm and Fabriano Acquarello 300gsm

1. boiling water pre shrinked for 10mins. Dried for a day.( no more speckles in the Arches)
2.Gelatin 3g to 500ml, cold water for 10 mins... Heated to 43 degree Celsius.
3.Added paper to the tray of gelatin for a minute, took excess gelatin off by sliding the paper on the side of the tray. Dried for the day. Stored the same Gelatin in the fridge
4.Reheated the gelatin the next day. Recoated the paper the same way. Dried.
Didnt add any hardner as yet, as I cant seem to get time to go buy any! :)

5ml 13% Pot Dich + 5ml Gum 35% + Windsor&Newton LAMP BLACK a very SMALL smudge! (coudnt get any Ivory black as yet, will do so..)

Coated paper, fan dried for 15mins.
Added a negative with squares 2% increments made in photoshop from white to black. Each 2% square has a number on it, which should clearly be seen when printed.

The sheet of Arches had 3 of the same negatives on it, each exposed 4, 6, and 8 mins. Just covered each negative when it passed the min mark.

Developed for 5 mins face down in room temp water.
Next tray developed for 5 mins face down in room temp water.
Next tray developed for 20mins same room temp water.

On the Arches paper I got:
What I got was NO staining in highlights or midtones or the whole paper. They looked ok though a little on the light side the tones came up.
Can read all the incremented 2% numbers in those areas.

The shadows are another business altogether, what I got was a massive yellow staining probably from the dichromate, plus it looked like a real mess as I couldnt really make out the incremental numbers from the negative. The mess seemed like too much watercolour overpigmented, its not one colour but just smudges of watercolour and yellow staining.
Reading Katharine suggestions, I'm thinking what I'm looking at could be OVERexposure? or the small Smudge I used from the lamp black is still too much pigment!?
I doubt it was caused by overcoating, as I turned each of the 3 negs upside down side by side, got the same result on each part of the print.
Could it be my sizing, and not using a hardner? Though the Highlights and Midtones look good?

I got kind of fed up looking at the yellow staining and used a 5% potassium metabisulfite solution, sprayed with a hand held spray gun. Didnt work as well, next time i'll use a tray bath.

The other Fabriano Aquarello paper I'll add more info on it later can't recall what it looked like, but had the same sort of problems as above.

I'll scan the prints when I get home and upload to a website.